Large scale flow separation and mesoscale eddy formation in the Algerian Basin

During the ELISA/MATER experiment floats released at about 600 m depth in the Levantine Intermediate Water layer south of Sardinia in July 1997 have revealed the existence of a coherent eddy, approximately 50 km in diameter and lasting for several months. This anticyclonic eddy was first observed south-west of Sardinia in November 1997 and drifted inside the Algerian Basin during the following months until April 1998. This eddy contained Levantine Intermediate Water at intermediate level and seemed to be related to 2 main large scale features: (a) a cyclonic gyre (250 km in diameter and 3–4 months period) located in the Algerian Basin and (b) a boundary current located along the continental slope south and west of Sardinia and originating from the Sardinia–Tunisia channel. We will first describe the “Sardinian” eddy, from a kinematical point of view, and the Algerian Gyre and second, give some insights about the eddy origin and its importance for LIW large scale spreading in the Western Mediterranean Sea

ATP induced MUC5AC release from human airways in vitro

Background: Chronic airway diseases are often associated with marked mucus production, however, little is known about the regulation of secretory activity by locally released endogenous mediators

The impact of freshening on phytoplankton production in the Pacific Arctic Ocean

International audienceSince the 1990s, drastic melting of sea ice and continental ice in the Arctic region, triggered by global warming, has caused substantial freshening of the Arctic Ocean. While several studies attempted to quantify the magnitude of this freshening, its consequences on primary producers remain poorly documented. In this study, we evaluate the impact of the freshwater content (FWC) of the upper Arctic Ocean on phytoplankton across the Pacific sector, from the Bering Strait (65°N) to the North Pole (86°N), during summer 2008. We performed statistical analyses on the physical, biogeochemical and biological data acquired during the CHINARE 2008 cruise to investigate the effect of sea-ice melting on the Arctic phytoplankton. We found that the strong freshening observed in the Canada Basin had a negative impact on primary producers as a result of the deepening of the nitracline and the establishment of a subsurface chlorophyll maximum (SCM). In contrast, regions with lower freshening, such as the Chukchi shelf and the marginal ice zone (MIZ) over the Chukchi Borderland, exhibited a shallower nitracline sustaining relatively high primary production and biomass. Our results imply that the predicted increase freshening in future years will likely cause the Arctic deep basin to become more oligotrophic because of weaker surface nutrient renewal from the subsurface ocean, despite higher light penetration

Phytoplankton distribution in the Western Arctic Ocean during a summer of exceptional ice retreat

International audienceA drastic ice decline in the Arctic Ocean, triggered by global warming, could generate rapid changes in the upper ocean layers. The ice retreat is particularly intense over the Canadian Basin where large ice free areas were observed since 2007. The CHINARE 2008 expedition was conducted in the Western Arctic (WA) ocean during a year of exceptional ice retreat (August-September 2008). This study investigates whether a significant reorganization of the primary producers in terms of species, biomass and productivity has to be observed in the WA as a result of the intense ice melting. Both pigments (HPLC) and taxonomy (microscopy) acquired in 2008 allowed to determine the phytoplanktonic distribution from Bering Strait (65° N) to extreme high latitudes over the Alpha Ridge (86° N) encompassing the Chukchi shelf, the Chukchi Borderland and the Canadian Basin. Two different types of phytoplankton communities were observed. Over the ice-free Chukchi shelf, relatively high chl-a concentrations (1-5 mg m-3) dominated by 80 % of diatoms. In the Canadian Basin, surface waters are oligotrophic (-3) and algal assemblages were dominated by haptophytes and diatoms while higher biomasses (~0.4 mg m-3) related to a deep Subsurface Chlorophyll Maximum (SCM) are associated to small-sized (nano and pico) phytoplankton. The ice melting onset allows to point out three different zones over the open basin: (i) the ice free condition characterized by deep and unproductive phytoplankton communities dominated by nanoplankton, (ii) an extended (78°-83° N) Active Melting Zone (AMZ) where light penetration associated to the stratification start off and enough nutrient availability drives to the highest biomass and primary production due to both diatoms and large flagellates, (iii) heavy ice conditions found north to 83° N allowing light limitation and consequently low biomass and primary production associated to pico and nanoplankton. To explain the poverty (Canadian Basin) and the richness (Chukchi shelf) of the WA, we explore the role of the nutrient-rich Pacific Waters, the bathymetry and two characteristics linked to the intense ice retreat: the stratification and the Surface Freshwater Layer (SFL). The freshwater accumulation induced a strong stratification limiting the nutrient input from the subsurface Pacific waters. This results in a biomass impoverishment of the well-lit layer and compels the phytoplankton to grow in subsurface. The phytoplankton distribution in the Chukchi Borderland and north Canadian Basin, during the summer of exceptional ice retreat (2008), suggested when compared to in-situ data from a more ice covered year (1994), recent changes with a decrease of the phytoplankton abundance while averaged biomass was similar. The 2008 obtained phytoplankton data in the WA provided a state of the ecosystem which will be useful to determine both past and future changes in relation with predicted sea ice decline